The European patent EP 1 240 709 B1 discloses a motor start circuit for a single phase induction motor with an running main winding and a start auxiliary winding, in which a switch connected in series with the auxiliary winding enables the AC to flow through the auxiliary winding to start the motor and then turns off the AC flowing through the auxiliary winding, as soon as the motor starts operating. A voltage sensor measures the motor voltage at the auxiliary winding or at main and auxiliary windings and generates a motor voltage signal representing the size of the measured motor voltage. The motor voltage signal is provided with a differentiator, which generates a dV/dT signal representing the time rate of the change of the motor voltage signal. A gate circuit, connected to a gate of the switch, receives the dV/dT signal and disconnects the switch, when the dV/dT signal reaches or exceeds a predetermined value. A preset timer disconnects the switch after the lapse of a predetermined period from the start of flow of motor current. Further, the U.S. Pat. No. 5,528,120 discloses a motor start circuit for a single phase AC induction motor, in which the start voltage of the measuring device is adjustable, for example in that the size of a variable resistance is changed. Further, U.S. Pat. No. 3,792,324 discloses a single phase motor, in which the current flow is stopped by the auxiliary winding, as soon as a measured current or voltage value exceeds a reference value. U.S. Pat. No. 6,982,539 B1 discloses a motor start circuit with a control circuit comprising a timer and a voltage sensor.